Electroluminescence occurs in semiconductor materials which are capable of emitting visible or near visible radiation when an electrical current passes through the semiconductor. Photoluminescence can also occur in these materials. If external light is used to excite the semiconductor, a characteristic wavelength of light is emitted. These characteristic wavelengths vary amongst different photoluminescent semiconductors and can be varied in a single semiconductor by doping or changing the composition of the material.
Amongst the various studies on the luminescence of photostimulated or electroluminescent materials is "Luminescent Photoelectrochemical Cells", Streckert, H. H., Tong, J. and Ellis, A. B., J. Am. Chem. Soc., Vol. 104, No. 2, 1982, pp. 581-588. It is noted therein that the intensity of light emitted by electroluminescence and photoluminescence varies directly with the applied voltage. The efficiency of charge transfer and good electrical contact at the surface is also noted as important in the efficiency of the process.
U.S. patent application Ser. No. 480,471 filed on Mar. 30, 1983 discloses semiconductor electrodes having multicolor luminescence. These semiconductors comprise solid state solutions of three elements which vary in a vertically anisotropic manner. The preferred solid state solutions are of cadmium, sulfur and selenium.
U.S. Pat. No. 4,211,586 discloses a method of forming a multicolor light-emitting array of diodes. The diodes are formed by differentially etching a graded n-type semiconductor and diffusing a p-type dopant into the surface of the n-type semiconductor to form a p-n junction diode.
U.S. patent application Ser. No. 712,799, filed Mar. 18, 1985, discloses an apparatus for detecting the presence of certain chemical compounds comprising a photoluminescent semiconductor having a metal coating on a radiation emitting surface of the semiconductor, a source of actinic radiation which can impinge on the radiation emitting surface of the semiconductor, and a means for detecting changes in the characteristics of radiation emitted from said radiation emitting surface. The absorption of hydrogen into the metal layer is suggested as varying the height of the Schottky barrier of the diode and causing a change in spectral characteristics of the radiation emitted.